JP3525150B2 - Method for manufacturing silicon carbide semiconductor substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a silicon carbide substrate for forming a semiconductor element.

[0002]

2. Description of the Related Art For the purpose of controlling high frequency and large power, a power semiconductor element (hereinafter referred to as a power device) using silicon (hereinafter referred to as Si) has been improved in performance by various means. . However, since the power device may be used in the presence of high temperature or radiation, the Si power device may not be usable under such conditions.

Further, in response to the demand for higher performance than Si power devices, the application of new materials is being studied. Silicon carbide (hereinafter Si)
The width of the forbidden band is 3.26e in 4H-SiC.
Since it has V2 and 6H-SiC of 3.02 eV), it has excellent controllability of electric conductivity at high temperature and radiation resistance, and has a dielectric breakdown voltage that is about an order of magnitude higher than Si. Is possible. Furthermore, since SiC has an electron saturation drift velocity that is about twice that of Si, it is also suitable for high-frequency, high-power control.

However, in order to apply the excellent physical properties of SiC to power devices, elemental technology as sophisticated as the process technology of Si is required. That is, after finishing the surface of the SiC substrate to a mirror surface, it is necessary to optimize the process conditions such as epitaxially growing a SiC thin film, doping a donor or an acceptor in the process, forming a metal film or an oxide film. .

The problem in epitaxial growth is to obtain a thin film having an intended carrier density and good crystallinity so that the characteristics of the device to be manufactured thereafter will be satisfactory. In the epitaxial growth of Si, a base plate (hereinafter referred to as a substrate) before growth is subjected to hydrochloric acid (hereinafter referred to as HCl) gas etching to make the surface of the substrate flat and clean. The characteristics of the Schottky diode manufactured by controlling the surface in this way are improved as compared with those without surface treatment.

On the other hand, in the epitaxial growth on SiC, heating in hydrogen (H ₂ ) is the most common surface treatment of the substrate. [For example, C. Hallin, ASBa
kin, F.Owman, P.Maertensson, O.Kordina, and E.Janze
n, "Silicon Carbide and Related Materials" Inst. of
Phys. Conf. Ser., No.142, 1996, pp.613-616]
Although etching with HCl has been attempted in a low concentration region, it has not been generally performed because it causes an etch pit. [For example, AABurk, Jr., LB Rowland,
J. Crystal Growth, vol.167, pp.586-595, (1996)]

[0007]

However, etching by heating in H ₂ has a problem that silicon droplets are generated on the surface. [Refer to the above-mentioned reference of AA Burk, Jr., LB Rowlan] In view of such a situation, an object of the present invention is to provide an optimum etching method as a treatment before epitaxial growth from the viewpoint of device characteristics.

[0008]

As described above, in the SiC technique, HCl etching before epitaxial growth has not been generally performed because it causes an etch pit. The inventor conducted experiments on the conditions of hot-gas phase etching of a substrate immediately before epitaxial growth, that is, the volume ratio and temperature when diluting HCl gas with H ₂ or argon (Ar), and as a result, in a high concentration region, We have found that HCl etching is effective.

In order to solve the above problems, the present invention provides a method of manufacturing a silicon carbide substrate for a semiconductor device, in which the surface of a silicon carbide base plate before epitaxial growth has a volume ratio of 6 %.
1300 to 15 in a hydrochloric acid gas atmosphere diluted to 15%
The epitaxial layer is grown by heating at 00 ° C. and performing vapor phase etching. By doing so, the substrate surface is cleaned and etched, and the crystallinity and film quality of the epitaxial layer such as carrier mobility are improved.

[0010] As the dilution gas, H ₂ or Ar is available.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Experiments and examples conducted for the present invention will be described below. [Experiment 1] First, an experiment was conducted on the HCl concentration. As a substrate (hereinafter referred to as a substrate) before epitaxial growth, a mirror-polished 4H-SiC single crystal was used, and a surface polished from the (0001) Si plane by tilting 8 degrees in the <1, 1, -2, 0> direction It was used.

First, the substrate is cut into 5 mm square chips by a dicer, washed with an organic solvent and an acid, and then the substrate is placed on a graphite susceptor coated with SiC with the Si surface to be etched up. The susceptor on which the substrate is placed is inserted into the quartz reaction tube and evacuated to a vacuum of 1 Pa or less. Next, vapor phase etching is performed. The vapor phase etching is H ₂ to H ₂ .
The mixture was heated at 1400 ° C for 5 minutes while flowing a mixed gas in which Cl gas was mixed at a flow rate of 10 to 150 mL per minute. The heating method for the susceptor is high frequency induction heating.

Subsequently, a SiC thin film is grown by the chemical vapor deposition method. H ₂ gas, monosilane gas (SiH ₄ ), propane gas (C ₃ H ₈ ) 3 L / min, 0.3 mL,
The mixture having a flow rate ratio of 0.25 mL is introduced into the reaction tube. In this state, it was heated at 1550 ° C. for 2 hours. Then, a 4H type SiC epitaxial layer grows on the substrate.

In order to evaluate the dislocation density of the grown film,
Etching was performed with potassium hydroxide (KOH). For this etching, a method of immersing the sample in KOH heated to 400 ° C. for 30 seconds in a Ni crucible was used. The defect density was counted by SEM observation. The carrier density of the epitaxial layer was 5 × 10 ¹⁵ cm ⁻³ . Figure 2 shows the etching conditions (HCl concentration) before epitaxial layer growth.
And shows the relationship between the etch pit density in the SiC epitaxial layer. From this figure, it can be seen that the etch pit density decreases as the HCl concentration (that is, the volume ratio) increases, and particularly when it exceeds 10%, the etch pit density decreases remarkably. The lowest etch pit density was exhibited at the highest concentration of 15% of the experiments.

The etch pits can be formed at the positions of dislocations which are linear defects in the epitaxial layer, and reflect the quality of crystallinity. Therefore, it can be concluded from the figure that the crystallinity of the growing epitaxial layer is improved as the HCl concentration during etching is increased, and is preferably 3% or more, more preferably 6% or more. [Experiment 2] Next, the relationship between the etching conditions and the mobility in the SiC epitaxial layer was investigated.

The experimental method will be described below. The method for producing a sample in which SiC was epitaxially grown was the same as in Example 1. As a method of evaluating the mobility of the epitaxial layer,
The vander Pauw method was used. That is, nickel (Ni) electrodes are formed at four corners on the epitaxial layer of the sample by the sputtering method using a metal mask. The diameter of the electrode is 2
The thickness is 00 μm and the thickness is 400 nm. After that, annealing is performed at 1050 ° C. for 5 minutes in an argon (Ar) atmosphere to obtain ohmic contact except for rectifying property.

FIG. 3 shows the relationship between the etching conditions before the growth of the epitaxial layer and the mobility in the SiC epitaxial layer. In the figure, it can be seen that the mobility rapidly increases as the HCl concentration increases and becomes saturated when the concentration exceeds 10%. That is, from the viewpoint of mobility, it is concluded that the higher the HCl concentration in the epitaxial layer growth pretreatment, the better, and the better it is 3% or more, and more desirably 6% or more. This is because the surface was sufficiently cleaned and etched before the epitaxial growth. It may also have a gettering effect on metal impurities found in silicon semiconductors.

Example A Schottky diode was manufactured for the purpose of investigating the direct influence of etching conditions on the device characteristics. The experimental method is described below. The substrate used and its cleaning method, the substrate etching method and the epitaxial growth method are the same as in Experiment 1. The Schottky diode was manufactured by the method described below.

First, Ni was sputtered on the back surface of a SiC substrate, and a back contact was formed by annealing at 1050 ° C. for 5 minutes in an Ar atmosphere. Next, Au was sputtered on the surface of the SiC epitaxial layer through a metal mask to form a Schottky electrode. The diameter of the Schottky electrode is 200 μm. Characteristics of Schottky diode fabricated in this way (Schottky barrier height, breakdown voltage)
And the etching conditions were investigated. The Schottky barrier height and breakdown voltage were obtained from the current-voltage (IV) curve. Figure 1
FIG. 6 is a characteristic diagram showing the HCl concentration dependence of both characteristics.

When the HCl concentration exceeds 3%, both the barrier height and the breakdown voltage increase. Furthermore, the barrier height gradually increases to 15%. Further, the breakdown voltage reaches about 520 V when the HCl concentration is 5% and is saturated thereafter. The value at 10% almost agrees with the design value of the element. From the above results, H
By setting the Cl concentration to 3% or higher, preferably 6% or higher, the crystallinity of the SiC semiconductor thin film and the characteristics of the semiconductor element can be improved.

Further, in the experiment and the example, only the result under the etching condition of 1400 ° C. is shown.
The same result was obtained in the range from 1 to 1500 ° C.
As for the growth surface, (0001) of 4H-SiC
Not only Si surface, 4H-SiC C surface or 6H-
It can also be applied to a Si surface of SiC, a C surface, or a surface obtained by inclining these surfaces at a minute angle.

[0022]

As described above, according to the present invention, S
The surface of the iC semiconductor substrate before epitaxial growth was diluted with a volume ratio of 6 to 15% in a hydrochloric acid gas atmosphere at 1300.
By heating to ˜1500 ° C. and performing vapor phase etching, the crystallinity of the growing epitaxial layer is improved,
The characteristics of the C semiconductor element can be improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between HCl concentration and Schottky diode characteristics (barrier height and breakdown voltage).

FIG. 2 is a characteristic diagram showing the relationship between HCl concentration and etch pit density.

FIG. 3 is a characteristic diagram showing the relationship between HCl concentration and thin film mobility.

Claims (2)

(57) [Claims] 1. A method of manufacturing a silicon carbide substrate for a semiconductor device, wherein the surface of a silicon carbide base plate before epitaxial growth is heated to 1300 to 1500 ° C. in a hydrochloric acid gas atmosphere diluted to a volume ratio of 6 to 15%. Heating, vapor etching,
A method for manufacturing a silicon carbide semiconductor substrate, which comprises growing an epitaxial layer. 2. The method for manufacturing a silicon carbide semiconductor substrate according to claim 1, wherein the diluent gas is hydrogen or argon.